Discovery and development of new materials for lithium ion batteries are increasing, with the goal of providing energy storage to, for example, electric and hybrid automotive applications throughout the world. Lithium ion (Li-ion) batteries remain a very important commercial and research focus. Owing to their superior power-density Li-ion batteries are used in a wide variety of applications. As the batteries become more powerful and utilized in diverse applications, thermal management becomes one of the central problems in their application. Charging and discharging of batteries generates considerable amounts of heat due to internal resistance, which in turn can effect battery performance, particularly for larger-scale batteries. Overheating and related safety concerns remain a major problem in battery design. In the case of discharging, the temperature rise is limited by the energy stored in cathode material. No such limit exists in the charging cycle when energy can be pumped even after full charging of the battery. In addition to Ohmic heating, chemical reactions that take place during charging and discharging in Li-ion batteries can also contribute to overheating. If overheating of the battery is not properly addressed, thermal runaway may cause a catastrophic destruction of the battery. From the other side, efficient heat removal from the battery allows for higher electrical currents to be achieved resulting in faster charging rates. These considerations explain the importance of thermal management for operation and safety of any kind of high-power batteries.
There are a number of commonly used methods for removal of the excessive heat from the batteries, e.g., increasing the air flow around the battery or maximizing the surface area of the electrodes. It has been also shown that the thermal effects associated with Li-ion intercalation and deintercalation can be efficiently addressed by the certain combinations of the cathode and anode materials. However, implementation of sophisticated engineered control methods for active cooling via enhanced air flow significantly increases the complexity of the battery design and its weight. The system level approaches cannot help with the localized hot spots and thermal gradients in the case of thick electrodes. The thermal and electrical gradients within the electrodes can lead to unbalanced charging and discharging resulting in lower energy storage capacity.
Improving the thermal conductivity of the electrodes themselves is an important step towards proper thermal management of the batteries. The latter is particularly important for Li-ion batteries because their performance strongly depends on the electrode temperature.
Conventional design of the electrodes involves mixing of the active materials with carbon black, conductive additives and polymer binders that provide the integrity for the electrodes and electrical connectivity. The problem with the carbon black-based electrodes, when used in high-power-density batteries, is their very low thermal conductivity (K), which reportedly is about 0.1 W/mK to about 2 W/mK at room temperature (RT). Such low values likely stem from poor heat conduction properties of amorphous carbon, which is K of about 0.1 to about 1 W/mK near RT, and the mechanical admixture-type structure of the electrodes, which introduces high thermal boundary resistance. The low thermal conductivity of the carbon black-based electrodes leads to their degradation as a result of undesired thermally-activated metal dissolution in the cathodes, or degradation of the solid electrolyte interface (SEI) layer at the anode surface.
There is an ongoing need for new electrode architectures with improved thermal conductivity properties relative to carbon black-based electrodes, for use in Li-ion electrochemical cells and batteries. The electrodes, electrochemical cells, and batteries described herein address this need.